最近在做一個 Android 項目，需要用到GPS獲取位置信息，從 API 查了一下，發現獲取位置信息僅需極其簡單的一句即可：
getLastKnownLocation(LocationManager.GPS_PROVIDER),
于是高興地不得了。可是一寫進代碼里，返回值（Location 類型）居然一直為null..郁悶的不得了。在網上查了好久，發現好多人都和我一樣糾結于這個問題上，有人說是因為GPS沒打開，也有人說是相關權限沒加上..可是我的明明已經在設置里打開，權限自然也加上了。在api上糾結了半天，終于找出原因了，原來要打開GPS其實在于這句：
setTestProviderEnabled("gps",true);
而跟手機上的設置沒多大關系（起碼在我的手機上測是這樣的）。手機上的設置關閉了，這一句照樣能打開；而即使手機設置打開了，沒這一句也是白搭。與這句對應的是
setTestProviderEnabled("gps",false);
用來關閉GPS.
GPS打開后可以用上面的方法獲取Location了嗎？還是不可以！確切地說是有時候可以，因為這個函數獲取的是上次已經獲得的位置信息，設想如果此程序第一次跑，先前并沒有獲取過位置信息，當然返回值為null了。經仔細查看api，在
requestLocationUpdates (String provider, long minTime, float minDistance, LocationListener listener)
里發現了這樣一句話：It may take a while to receive the most recent location. If an immediate location is required, applications may use the getLastKnownLocation(String) method. 因此為了獲取位置信息，應該用此方法為manager設置監聽器，在監聽器中onLocationChanged(Location location)里獲取。
測試代碼如下：
public void onLocationChanged(Location location)
{
Log.i("onLocationChanged", "come in");
if (location != null)
{
Log.w("Location","Current altitude = "+ location.getAltitude());
Log.w("Location","Current latitude = "+ location.getLatitude());
}
}
經過測試，經過一段時間后可以獲取Location（獲取時間與minTime、minDistance相關）。還需注意的一個問題是在設置了監聽器后，刪除監聽器之前不能用上面的方法關閉gps，否則會報錯。因此關閉gps的方法是
manager.removeUpdates (listener);//listener 即為監聽器實例
manager.setTestProviderEnabled("gps",false);
以下是測試代碼，所需權限有：
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"></uses-permission>
<uses-permission android:name="android.permission.ACCESS_MOCK_LOCATION"></uses-permission>
<uses-permission android:name="android.permission.UPDATE_DEVICE_STATS"></uses-permission>
import android.app.Activity;
import android.content.Context;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.util.Log;
public class audio extends Activity
{
/** Called when the activity is first created. */
LocationManager locationManager;
LocationListener llistener;
String provider;
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Criteria criteria = new Criteria();
criteria.setAccuracy(Criteria.ACCURACY_FINE);
criteria.setAltitudeRequired(false);
criteria.setBearingRequired(false);
criteria.setCostAllowed(true);
criteria.setPowerRequirement(Criteria.POWER_LOW);
String serviceName = Context.LOCATION_SERVICE;
locationManager = (LocationManager) getSystemService(serviceName);
locationManager.setTestProviderEnabled("gps", true);
provider = locationManager.getBestProvider(criteria, true);
Log.d("provider", provider);
llistener = new LocationListener() {
@Override
public void onLocationChanged(Location location)
{
// TODO Auto-generated method stub
Log.i("onLocationChanged", "come in");
if (location != null)
{
Log.w("Location", "Current altitude = "
+ location.getAltitude());
Log.w("Location", "Current latitude = "
+ location.getLatitude());
}
locationManager.removeUpdates(this);
locationManager.setTestProviderEnabled(provider, false);
}
@Override
public void onProviderDisabled(String provider)
{
// TODO Auto-generated method stub
Log.i("onProviderDisabled", "come in");
}
@Override
public void onProviderEnabled(String provider)
{
// TODO Auto-generated method stub
Log.i("onProviderEnabled", "come in");
}
@Override
public void onStatusChanged(String provider, int status,
Bundle extras)
{
// TODO Auto-generated method stub
Log.i("onStatusChanged", "come in");
}
};
locationManager.requestLocationUpdates(provider, 1000, (float) 1000.0, llistener);
}
protected void onDestroy()
{
locationManager.removeUpdates(llistener);
locationManager.setTestProviderEnabled(provider, false);
super.onDestroy();
}
